Much has been learned in recent years concerning the microbial and biochemical composition of plaque, and its importance in the etiology of dental caries is well documented. However, relatively little is known still about how plaque is formed. Two important aspects of plaque formation are the highly specific nature of bacterial colonization on the tooth surface, and the key role that certain salivary proteins play in interbacterial attachment, or aggregation, in the development of the enamel pellicle, and in the adhesion of specific bacteria to the surface of the tooth. Our objective is to study the basic molecular interactions that give rise to the adhesive phenomena and to apply these findings to the modification of plaque and the processes that contribute to its formation. The proposal outlines studies for the isolation and characterization of the specific salivary aggregating factors and the surface receptors from strains of Streptococcus sanguis and S. mitis. The sanguis-specific factor has been purified with the use of sucrose density gradient centrifugation and isoelectric focusing and has been resolved into what appear to be non-identical macromolecular subunits. The receptor for the salivary factor has been solubilized from the cell wall of S. sanguis and is in the process of being further purified and studies. The isolated factor and receptor will be used in studies to determine the mechanisms that form the basis for bacterial adhesion and aggregation.